Various apparatus and methods have been previously proposed for pre-heating water in a water heater or water storage tank using refrigerant from air conditioning apparatus such as an air conditioner with a non-reversible refrigerant circuit, a heat pump for a residential air conditioning system having a reversible refrigerant circuit, and a roof top unit (RTU) commercial system that operates in an air-cooling only mode but that has a valve to alternatively direct refrigerant flow from a compressor either to an air-cooled condenser or to a water-cooled condenser/heat exchanger that exchanges heat from refrigerant used in providing cooled air to a commercial building's interior to water from the commercial building's water heating system.